Elastomeric swaging is a process used to fasten end fittings onto tubes of steel, aluminum, copper or other deformable metals. This is commonly done by assembling a split steel anti-extrusion ring, an elastomeric expander sheath, another split steel ring and a bushing onto a drawbolt with an expanded head portion. This drawbolt assembly is positioned in the tube end, inserted in an end fitting and placed in the swaging die. The drawbolt is pulled towards or pushed against the bushing forcing the elastomeric sheath to compress and expand outward into the tube, forcing the tube into the grooves of the fitting. One such process and apparatus is described in U.S. Pat. No. 4,043,160, assigned to the assignee hereof.
During swaging, substantial force is exerted on the split steel rings. Generally, this does not cause a problem when swaging steel tubes, however the dislocation of these rings causes unacceptable scratching, cutting and nicking on the insides of softer metal tubes. We have also found that these split rings must be replaced every 10 to 15 cycles when swaging aluminum tubes.
In an effort to solve these problems, many different sizes, shapes and materials have been tried for anti-extrusion rings. Nylon anti-extrusion rings eliminated scoring inside aluminum and other soft metal tubes, but the rings were too long, sacrificing the useful length of the elastomeric expander. Short nylon anti-extrusion rings were also tried but failed after one or two swages due to pressure and temperature during swaging operations. Rectangular steel anti-extrusion rings lasted longer, but the softer metal tubes were still damaged. Different metals were tried for the split rings, but none provided substantially better results for production applications.